Numerous systems have already been used to burn carbonaceous materials. It is known, inter alia, to use for this purpose fluidized-bed reactors operated as described hereinbefore (see British Patent Specification No. 784,595 and articles by J. R. GRACE, "Fluidization and its Application to Coal Treatment and Allied Processes", AICHE Symposium Series 141, Vol. 70 (1974), pp. 21-26, and D. L. KEAIRNS et al, "Design of a Fluidized Bed Combustion Boiler for Industrial Steam Generation", AICHE Symposium Series 126, Vol. 68 (1972), pp. 259-266).
The known processes have the disadvantages that the height of the bed must be comparatively low so that the pressure loss is kept within reasonable limits, that the presence of cooling surfaces in the lower part of reactor space involves a disturbance of the transverse mixing of the solids in the fluidized bed so that the inhomogeneities of temperature (overheating, formation of crusts) occur, and that the operation of the reactor cannot be satisfactorily adapted to varying power requirements. An adaptation can be effected virtually only by a decrease in temperature although this involves poorer combustion and fluidization conditions, or by a shut-down of individual reactor units.